The invention relates to a bearing arrangement for a spinning shaft of an open-end spinning rotor of the type provided with a spinning rotor at one end and a driving whorl at the other end. The spinning shaft is mounted in a bushing with two roller bearings having their roller elements running directly upon it, and having associated with it an oil-feed device dispensing oil dropwise in the area between the two roller bearings.
In a known bearing of the type mentioned hereinabove (German Auslegeschrift No. 2,333,555), a deep-groove ball bearing is provided on the portion of the shaft closest to and facing the spinning rotor and a guidance-free roller bearing is provided on the side (portion of the shaft) away from the spinning rotor. The balls of the deep-groove ball bearing run in a groove in the shaft (inner race) and in an outer ring or race, mounted tightly in a bushing. An outer ring, likewise mounted tightly in the bushing, is provided for the rollers of the roller ball bearing. Since the roller bearing is not required to accept any axial loads, greater torques are produced in the radial direction. In order to increase the lifetime of such a bearing, it is provided that the normal conventional grease lubrication may be replaced by an oil lubrication. An oil-feed device is provided for this purpose, said device being disposed in the area between the roller bearings and dispensing oil to the shaft dropwise. The oil-feed device contains a wick which is submerged in the oil reservoir and extends to the vicinity of the shaft. The amount of oil dispensed in this device depends on the distance between the oil reservoir and the shaft and upon the cross section of the wick. It appears very difficult if not impossible to meter the oil feed in this design in such manner that it corresponds to the actual oil requirement of the two roller bearings. In this design, oil continues to be supplied even when the spinning rotor is stopped for a period of time, and, when the spinning rotor of a spinning assembly or the entire spinning machine has been stopped for a long period of time, this can result in a considerable amount of excess oil being supplied, which is unacceptable in practice.
An object of the invention is to provide oil lubrication for a bearing of the type described hereinabove, said lubrication making possible an exact metering of the oil to be supplied in accordance with the requirements of the roller bearings. The invention contemplates providing that the oil-feed device comprises a sealing element facing the shaft, said sealing element dispensing oil only at a preset pressure differential which depends upon the operating state of the spinning rotor.
This design of the present invention makes it possible to adjust the volume of oil and the pressure differential exactly with respect to one another so that very exact metering is achieved. In additon, it is ensured that when the spinning rotor is stopped, no oil is supplied, since there is then no pressure differential. This has the advantage that when the spinning assembly or the entire machine is stopped, no unnecessary oil is supplied, which could result in excess oil being supplied. In addition, the oil feed is designed so that the amount of oil which is centrifuged out of the grease lubrication of the roller bearing as a result of the high rotational speed is replaced.
In an advantageous embodiment of the invention, means are provided for the sealing element to face the shaft with a surface which forms a groove with the circumference of the shaft which widens in the rotation direction of the shaft. In this widening groove, a negative pressure is produced by the rotation of the shaft whose magnitude is a function of the rotational speed of the shaft and the geometric shape of the groove. This negative pressure serves to enable the shaft to draw the oil it requires for its bearings.
In another preferred embodiment of the invention, means are provided for the sealing element to consist of a porous material whose porosity is adjusted to the viscosity of the oil in such manner that the sealing element dispenses a specified volume of oil at a preset pressure differential. This design has the advantage that no control or regulating processes controllable externally are required to maintain or meter oil lubrication. The manufacturing cost also remains within tolerable limits.
In accordance with one important feature of preferred embodiments of the invention, it is provided that the shaft has a diameter in the area between the roller bearings and particularly in the area of the sealing element of the oil-feed device which is larger than the races of the ball bearings. In this way it is possible for the oil dropping on the shaft to be flung off and atomized at higher circumferential velocities. In addition, the advantage is gained that the critical rotational speed of the bearing can be adjusted so that it is above the operating speed of 45,000 min.sup.-1 for example.
In order to have the largest possible roller elements and therefore smaller roller element and cage speeds, means are advantageously provided such that races for the roller elements are machined into the inner surface of the bushings. It has been found advantageous if each roller bearing has five balls as roller elements, the diameter of said balls being at least 50% of the diameter of the corresponding races (grooves) of the shaft. In this design, it is possible to have large roller bearing balls while the outside dimensions of the bearing bushing remain the same.
In accordance with another important feature of preferred embodiments of the invention, means are provided such that the bushing is supported in a housing with at least one intermediate bushing to absorb impact and vibration, said intermediate bushing extending in the axial direction from the vicinity of the whorl to approximately the center of the bushing. It is also advantageous to have at least two intermediate bushings disposed concentrically to one another between the busing and the housing, said intermediate bushings being made of materials with different properties. This makes it possible on the one hand to reduce the bearing load and on the other hand to limit the possible wobbling of the shaft and hence of the spinning rotor.
In accordance with yet another feature of preferred embodiments of the invention, means are provided such that the oil reservoir is located in an encapsulated housing, provided with a metered, throttled air supply. In this design, a negative pressure then develops inside the housing when oil is removed. When this negative pressure reaches the same value as the negative pressure on the outside of the sealing element, the oil feed will be interrupted until the pressure inside the housing has decreased once more. This results in periodic oil feed and also ensures that no oil is fed when the spinning rotor is stopped.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.